The present invention relates to a gate controlled semiconductor device providing control of a large power signal with small control signals.
The field of application of the invention relates to power control circuits, where it is important to control and switch large power signals with very small control signals, such as for example at the interface between data processing microelectronics and controlled power circuits, or at connection points between different circuits, for example in telecommunications, telephone technology, or in controlled drives for electric motors, or in power supplies.
Conventionally controlled semiconductor devices which include pnpn-type switches are thyristors (silicon controlled rectifiers). Such known pnpn-type switches are bipolar devices with a layer sequence n.sup.+ pnp.sup.+, which are provided with external contacts at the n.sup.+ -layer (cathode), the p.sup.+ -layer (anode) and at the inner p-layer (anode gate), and more rarely at the inner n-layer (control gate). These bipolar devices show symmetrical characteristics. However, they can be connected in an antiparallel circuit within a semiconductive layered body to form symmetrically acting devices, such as, for example, triacs. Thyristors, when connected to a reverse voltage (a negative anode voltage) below their breakdown point, block current in either direction. Only with a positive anode voltage and after the application of a triggering signal to the control gate, is the thyristor switched over into a highly conductive state.
It is disadvantageous however, that relatively large currents and powers are required at the control gate, and after triggering, the control gate becomes ineffective. The conducting state of these pnpn-type switches can be interrupted only with difficulty, and interruption or reversal of the anode voltage is necessary for this purpose.
Known is also a thyristor employing an insulated gate and being based on the known design of the double-diffusion-MIS-field effect-transistor (DMOS-transistor), which by the addition of one or two diffusion areas is modified to a symmetrical pnpn-type switch or respectively, to a two-directional pnpn-type switch.
It is true that the latter pnpn-type switch or thyristor provides the possibility of a nearly power-free turning-on but its conducting condition is not completely controllable by the gate electrode. Consequently, this pnpn-type switch needs an additional current interruption circuit having the disadvantages described above.
The interruptor circuit, which comprises MIS- and bipolar transistors, can be integrated in the pnpn-type switch. This measure, however, would again be disadvantageous for the application in power switching devices.